Early signs of prostate cancer

A reliable early warning sign for prostate cancer has eluded researchers so far - but the results of a new study go a step closer towards finding one.

The study, conducted by teams in Stockholm and Boston, looked at the relationship between prostate-specific antigen, or PSA (the chemical currently used as a 'marker' for prostate cancer progression), and two other blood proteins.

It found that men with prostate cancer which could not be detected by the PSA test could potentially be picked up by measuring levels of the two other proteins - called insulin-like growth factor 1 (IGF-1) and insulin-like growth factor binding protein 3 (IGFBP-3).

The authors of the study, published in The Lancet, say that further studies are urgently needed to confirm their findings.

Prostate cancer is the most common cancer in Australian men over 55, but there is no single test that is sufficiently accurate to justify a program of screening all men in this age group. Current guidelines, set by the NH&MRC, advise that only men with symptoms (such as problems with urinating, or blood in the urine) be tested. The first stage of testing includes both a rectal examination and a blood test for PSA levels. A diagnosis of prostate cancer is then confirmed or excluded using a biopsy.

Many doctors and lobby groups have called for a program of mass screening for prostate cancer in older men, just as mammograms are recommended to detect breast cancer in women over 50. The reason mass screening has not been implemented is that research shows it does not lower death rates from the disease.

This is partly because many of the cancers that would be detected through mass screening would not be deadly anyway: two-thirds of prostate cancer cases are not life-threatening.

But the other problem is that neither the rectal examination nor the PSA test is 100% accurate, so some cancers would not be picked up. In the Stockholm-based study, for example, 50 out of 209 men with newly diagnosed prostate cancer had normal PSA levels, and so would not have been picked up through a PSA test.

That same group of men, however, had other potential cancer indicators: their levels of the protein IGF-1 were higher than those of a similar group of men who were cancer-free, and their levels of IGFBP-3 were lower. Furthermore, while levels of IGF-1 were high for all men with prostate cancer, low levels of IGFBP-3 were found only in those with low PSA levels.

Low levels of IGFBP-3 and high levels of IGF-1, the researchers suggest, might therefore be used to design a more sensitive test for prostate cancer: one that would identify cases that would not be detected through a PSA test alone.

Low levels of IGFBP-3 might also identify men at high risk of developing prostate cancer in the future, they speculate, though larger, more systematic studies are first needed to verify their results.